Study on influence of mechanical stirring on heat transfer characteristics during jet heating of crude oil storage tank

doi:10.11949/0438-1157.20230006

Abstract

Abstract:

The physical and mathematical models of heat transfer and flow processes in a large floating roof storage tank under the synergy of jet heating and mechanical stirring were established. The sliding grid technique was used to model the stirring impeller. The flow and heat transfer laws of strong and weak buoyant jet heating processes were numerically simulated based on the finite volume method (FVM). The results show that compared with the strong buoyancy jet, the heating rate of the weak buoyancy jet can be increased by 74%, and the heating time required to reach the same temperature can be shortened by 42%. For the strong buoyant jet heating process, the increase of mechanical stirring can significantly increase the overall velocity in the computational domain, enhance the heat exchange between hot and cold media, increase the heating rate by 9.6%. It can also make more uniform oil temperature distribution in the computational domain and a 17% reduction in temperature variance. For the weak buoyancy jet heating process, although increasing the stirring effect can only increase the heating rate by 0.9%, it can reduce the temperature variance by 29%. Mechanical stirring has a more significant effect on the heating rate of strong buoyant jet and the temperature uniform distribution of weak buoyant jet. It is found that mechanical stirring can increase the heating efficiency of strong buoyant jet by 0.7%. In addition, further studies have found that the installation height of agitator plays an important function in eliminating the low-temperature area at the bottom of the actual storage tank and regulating the oil temperature distribution. The numerical simulation results can provide a significant reference for the structural design of mechanical agitator.

Key words: numerical simulation, jet heating, mechanical stirring, heat transfer, flow

摘要：

以射流加热和机械搅拌协同作用下，大型浮顶储油罐内的传热和流动过程为研究对象构建物理和数学模型，并采用滑移网格技术对搅拌叶轮作用区域建模，基于有限体积法对强、弱浮力射流加热过程的流动和传热规律进行了数值模拟研究。结果表明：相比强浮力射流，弱浮力射流加热时的升温速率可提升74%，达到相同温度所需的加热时间缩短42%。对于强浮力射流加热过程，增加机械搅拌可以使计算域内的整体速度显著升高，加强冷热介质间的热交换，使升温速率提高9.6%，也可令计算域内的油温分布更加均匀，温度方差降低17%。对于弱浮力射流加热过程，增加搅拌作用虽仅可令升温速率提高0.9%，但可使温度方差降低29%。机械搅拌对强浮力射流加热时的升温速率提升更显著，而对弱浮力射流加热时促使温度均匀分布的效果更显著，同时发现机械搅拌可使强浮力射流的加热效率提升0.7%。此外，进一步研究发现搅拌器的安装高度对于消除实际储罐底部的低温区域、调控油温分布具有重要作用，数值模拟结果可以为机械搅拌器的结构设计提供重要的参考依据。

关键词: 数值模拟, 射流加热, 机械搅拌, 传热, 流动

CLC Number:

TE 821

Jian ZHAO, Xingchao ZHOU, Dan XIA, Hang DONG. Study on influence of mechanical stirring on heat transfer characteristics during jet heating of crude oil storage tank[J]. CIESC Journal, 2023, 74(5): 1982-1999.

赵健, 周兴超, 夏丹, 董航. 机械搅拌对原油储罐射流加热过程传热特性的影响规律研究[J]. 化工学报, 2023, 74(5): 1982-1999.

Figures/Tables 22

Table 1 Relevant physical parameters of boundary materials

固体介质	密度/(kg/m³)	热导率/ (W/(m·℃))	比热容/(J/(kg·℃))
罐顶及空气层	1.225	1.05	1006
罐壁保温层	60	0.055	800
罐底土壤	1600	1.74	1750

Table 2 Model establishment parameters

参数	数值
罐体高度/m	5
罐体直径/m	12
射流加热管直径/mm	219
喷嘴高度/mm	160
弯管直径/mm	70
转弯半径/mm	50
喷嘴直径/mm	40
喷嘴数量	6
弯管角度/(°)	45
叶轮直径/mm	500
叶轮高度/mm	750
射流加热管高度/mm	600

Fig.1 Schematic diagram of the thermal system

Fig.2 Grid system for numerical computation

Table 3 Different grid design schemes

网格系统编号	最小网格尺寸/mm	最大网格尺寸/mm	网格增长率	网格数量/个	计算时间/h
1	4	220	1.2	401249	1.38
2	3	180	1.2	1188348	2.78
3	2	150	1.2	1986504	3.48
4	1	130	1.2	2548828	4.08
5	0.5	110	1.2	3276792	4.83

Fig.3 Changes of Nusselt number of heating tube with time under different grid sizes

Table 4 Comparison of temperature data under experiment and numerical simulation

序号	距罐中心距离/mm	距罐底距离/mm	数值模拟温度/℃	实际测量温度/℃	相对偏差/%
1	0	10	27.150	28.9	6.06
2	0	30	27.856	28.3	1.57
3	0	130	27.899	28.0	0.36
4	0	200	27.921	28.4	1.69
5	0	270	28.356	29.7	4.53
6	150	10	27.350	28.1	2.67
7	150	30	27.279	27.8	1.87
8	150	130	27.269	28.3	3.64
9	150	200	27.451	28.2	2.66
10	150	270	27.945	29.6	5.59
11	260	10	27.153	28.4	4.39
12	260	30	27.494	28.1	2.16
13	260	130	27.656	28.5	2.96
14	260	200	28.110	28.6	1.71
15	260	270	29.157	29.8	2.16
16	380	10	27.025	28.1	3.83
17	380	30	27.980	28.2	0.78
18	380	130	28.098	28.5	1.41
19	380	200	28.021	28.1	0.28
20	380	270	27.081	29.2	7.26

Fig.4 Changes of average velocity near the agitator with time

Table 5 Parameters of simulated working conditions

工况	搅拌速度/(r/min)	初始温度/℃	射流温度/℃	射流速度/(m/s)	Fr	M₀	B₀	射流类型
1	0	40	70	0.1	0.63	1.26×10^-5	2.94×10^-5	强浮力
2	350	40	70	0.1	0.63	1.26×10^-5	2.94×10^-5	强浮力
3	0	40	50	1.0	10.3	1.26×10^-3	7.72×10^-4	弱浮力
4	350	40	50	1.0	10.3	1.26×10^-3	7.72×10^-4	弱浮力

Fig.5 Selection of observation lines and sections inside the tank

Fig.6 Comparison of the three-dimensional temperature field at t=4 h during heating of a strong buoyant jet with or without mechanical stirring

Fig.7 Comparison of the three-dimensional velocity field at t=4 h during heating of a strong buoyant jet with or without mechanical stirring

Fig.8 Changes of temperature with time on center line l0

Fig.9 Radial temperature distribution of different liquid levels at t=4 h

Fig.10 Comparison of the three-dimensional temperature field at t=2.5 h during heating of a weak buoyant jet with or without mechanical stirring

Fig.11 Comparison of the three-dimensional velocity field at t=2.5 h during heating of a weak buoyant jet with or without mechanical stirring

Fig.12 Changes of temperature with time on center line l0

Fig.13 Radial temperature distribution of different liquid levels at t=2.5 h

Fig.14 Changes of average temperature with time

Fig.15 Changes of temperature variance with time

Fig.16 Changes of boundary heat dissipation of computational domain with time

Fig.17 Changes of jet heating efficiency with time

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